Balchandani Priti, Spielman Daniel
Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
Magn Reson Med. 2008 May;59(5):980-8. doi: 10.1002/mrm.21537.
Proton magnetic resonance spectroscopic imaging ((1)H MRSI) at 7T offers many advantages, including increased SNR and spectral resolution. However, technical difficulties associated with operating at high fields, such as increased B(1) and B(0) inhomogeneity, severe chemical shift localization error, and converging T(1) values, make the suppression of the broad lipid peaks which can obscure targeted metabolite signals, particularly challenging. Conventional short tau inversion recovery can successfully suppress fat without restricting the selected volume, but only with significant metabolite signal loss. In this work, we have designed two new pulses for frequency-selective inversion recovery that achieve B(1)-insensitive fat suppression without degrading the signal from the major metabolites of interest. The first is a spectrally selective adiabatic pulse to be used in a volumetric (1)H MRSI sequence and the second is a spatial-spectral adiabatic pulse geared toward multi-slice (1)H MRSI. Partial interior volume selection may be used in addition to the pulses, to exclude areas with severe B(0) inhomogeneity. Some differences in the spectral profile as well as degree of suppression make each pulse valuable for different applications. 7T phantom and in vivo data show that both pulses significantly suppress fat, while leaving most of the metabolite signal intact.
7T 质子磁共振波谱成像（(1)H MRSI）具有诸多优势，包括提高信噪比和光谱分辨率。然而，在高场强下操作会遇到技术难题，如 B(1) 和 B(0) 不均匀性增加、严重的化学位移定位误差以及 T(1) 值收敛，这使得抑制可能掩盖目标代谢物信号的宽脂质峰极具挑战性。传统的短 tau 反转恢复序列可以成功抑制脂肪，且不限制选定的体积，但会导致显著的代谢物信号损失。在这项工作中，我们设计了两种用于频率选择性反转恢复的新脉冲，可实现对 B(1) 不敏感的脂肪抑制，同时不会降低感兴趣的主要代谢物的信号。第一种是用于容积式(1)H MRSI 序列的光谱选择性绝热脉冲，第二种是适用于多层(1)H MRSI 的空间光谱绝热脉冲。除了这些脉冲外，还可使用部分内部体积选择来排除 B(0) 不均匀性严重的区域。光谱轮廓和抑制程度的一些差异使得每个脉冲在不同应用中都很有价值。7T 体模和体内数据表明，这两种脉冲都能显著抑制脂肪，同时大部分代谢物信号保持完整。
